1. Field of the Invention
This invention relates to a facsimile apparatus connected to an ISDN (an integrated series digital network).
2. Description of the Prior Art
An ISDN makes feasible a communication network employing digital transmission in place of a telephone-oriented communication network based on analog transmission, and it provides multifarious communication services such as telephone and facsimile communication and data communication services. The ISDN interface specifications are stipulated by an I-series advisory of the CCITT.
Services provided by a low-level function of an ISDN include services referred to as a "bearer services" defined by CCITT advisory 1.211. Among these, a 3.1 KHz audio service is used in data signal transmission of the 3.1 KHz band such as that of a G3 facsimile. A 64 KHz unlimited digital service is used in digital signal transmission such as that of a G4 facsimile.
FIG. 6 is a block diagram illustrating the manner in which a conventional G3 facsimile apparatus 61 is connected to a network terminating device NT 63 via a terminal adapter 62. Here the G3 facsimile apparatus 61 is connected to the terminal adapter 62 via a line connection terminal, the terminal adapter 62 is connected to the network terminating set NT 63 at a reference point T, and the network terminating set NT 63 is connected to an ISDN 64.
The terminal adapter 62 detects a current loop between itself and the G3 facsimile apparatus 61, identifies an inputted dial signal, subjects a signal received from the facsimile apparatus 61 to an A/D conversion and outputs the converted signal to the ISDN 64 via a B channel. On the other hand, when data is received from the ISDN 64 via the B data channel, the terminal adapter 62 converts this digital data into an analog signal and forms a current loop between itself and the G3 facsimile apparatus 61, and the received facsimile signal is reproduced by the G3 facsimile apparatus 61.
Thus, in the prior art, such a terminal adapter is necessary in order to connect a G3 facsimile apparatus, which is a subscriber's apparatus for non-ISDN use, as a subscriber's apparatus for ISDN. Another problem is that with a basic access interface, a maximum of only eight subscriber's apparatus (e.g., facsimile apparatus) can be connected to one set of wiring.